"Plankowner is a term used by the United States Navy, and has consequently been variously defined by different units. The origin of the term is the implication that a crew member was around when the ship was being built and commissioned, and therefore has bragging rights to the "ownership" of one of the planks in the main deck."
Crabman (or Nambarc, whichever applies), being a boat driver, this term would be right down his alley (wave). In this case it means some of the original folks that started the forum.